Mark, 47, was also fined and ordered to carry out 120 hours of unpaid work in the community.

Last night, as an MP criticised the magistrates, Mrs Higgins - who has run the pet shop for 28 years - said the family's eight-month ordeal had left them traumatised.

She added: 'It's ridiculous. I mean, what danger am I that I have to wear an electronic tag? These last few months have been a very stressful time.'

The seven-week curfew imposed by the court means she is unable to babysit her great-grandson at his home or go to bingo sessions with her sister, and will be unable to attend a Rod Stewart concert after tickets were bought for her by her nephew, actor Will Mellor.

Joan Higgins, 66, and her son Mark, 47, have both been ordered to pay fines after selling a goldfish to a 14-year-old boy

Her son said: 'I think it's a farce. What gets me so cross is that they put my Mum on a tag - she's nearly 70, for goodness' sake.

'She's a great-grandma so she won't be able to babysit a newborn baby. You would think they have better things to do with their time and money.'

Mr Higgins claimed the undercover operation was a clear case of entrapment - when a person is encouraged by someone in some official capacity to commit a crime - and said the case should never have gone to court.

He said: 'The council sent the 14-year-old in to us. It is hard to tell how old a lad is these days. He looked much older than 14.'

He added that his mother almost fainted in the dock when magistrates told her she could go to prison for the offence.

'I told her they wouldn't send her to prison but she was still worried,' he said. 'The only other time she has been in court is when she did jury service.'

Under the Animal Welfare Act 2006 it is illegal to sell pets - including goldfish - to children under the age of 16 unless they are accompanied by an adult. Pet shops must also provide advice on animal welfare to buyers.

The maximum penalty is imprisonment for up to 12 months, or a fine of up to £20,000, or both.

The Higgins family's ordeal began when council officials heard that Majors Pet Shop in Sale, Greater Manchester, was selling animals to children.

They sent the 14-year-old schoolboy into the shop to carry out a test purchase and Mr Higgins sold him the goldfish without questioning his age or providing any information about the care of the fish.

A council officer in the shop at the time also noticed a cockatiel in a cage that appeared to be in a poor state of health. A vet found the bird had a broken leg and eye problems. It was later put down.

She had intended to take it to the vet but had been distracted and worried because her other son was in hospital.

The court heard that Mrs Higgins had possessed a licence to sell animals for many years and had never had any problems before.

She was fined £1,000 and given a community order with a curfew requiring her to stay home between 6pm and 7am for seven weeks.

Mrs Higgins did not have her licence to sell animals removed, but both she and her son were told that if they ever appeared in court for a similar offence they could face a jail sentence.

David Davies, Tory MP for Monmouth, said: 'You simply couldn't make it up. It is absolutely ludicrous that old ladies should be hounded through the courts and electronically tagged for something like this.

'At a time when courts are being told not to lock up career burglars we have them issuing severe punishments like this on little old ladies.' Mr Davies, who has served as a special constable for three years, said: 'Not only is it traumatic for her but it is a complete waste of time and taxpayers' money. It is ridiculous.

'Instead of getting 14-year-old boys to act in this type of sting they should have them trying to nail people who sell drugs outside our schools.'

Trafford Council said it launched an investigation after an unsubstantiated complaint that the shop had sold a gerbil to a 14-year-old girl with learning disabilities. The council claimed the animal later died after the child placed it in a disposable coffee cup with a plastic lid on top.

But the complaint did not form part of the legal action in court and its truth cannot be verified.

Mrs Higgins said the shop had not stocked gerbils for months before the complaint anyway.

Defending the goldfish case, Iain Veitch, head of public protection at Trafford Council, said: 'The evidence presented for this conviction clearly demonstrates that it is irresponsible to sell animals to those who are not old enough to look after them.

'Let this conviction send out a message that we will not tolerate those who cause unnecessary suffering to animals. The council will always try to support pet and business owners so that they are able to care for their animals properly, but where they continually ignore the advice they are given, we will not hesitate to use our statutory powers.'

The goldfish was later adopted by an animal welfare officer and is in good health.